The present invention relates to a liquid level sensor switch for electrically detecting the drop of liquid level lower than a specified level.
In general, a typical liquid level sensor switch of this kind is installed for example in an oil reservoir of a portable power generator engine so as to be actuated upon detection of the specified low level of oil in the reservoir.
A conventional liquid level sensor switch is constructed, as shown in FIG. 12. This device comprises a case 1 incorporating a rod type guide 2 vertically extending from the inside bottom of the case and a float 4 having a center bore 3 and movably mounted on the guide 2 with a gap s around the guide 2 in the float center bore so as to enable the float 4 to move up and down along the guide 2 inside the case 1. The float has an electrode plate 5 attached to the ring-shaped bottom of the float. Paired fixed contacts 6 and 7 are secured onto the inside bottom of the case 1 and disposed opposite to each other with the guide 2 between them. The float 4 moves down with the drop of oil in the case. When the float 4 moves down to put the electrode plate 5 into contact with both the paired contacts 6 and 7, the bridged contact circuit is turned on to produce an electric signal indicative of the oil level being lower than a specified level.
When the portable power generator is used on a slope, the above-described liquid level switch cannot detect the specified level of the oil because the float 4 inclines aside with its center bore 3 abutting on the side surface of the guide 2 as shown in FIG. 13 due to the presence of a gap S between the guide 4 and the center bore of the float 4 and the electrode plate 5 attached to the bottom surface of the float 4 can not get contact with one (contact 7 in the shown case) of the paired fixed contact 6, 7 having a variation ε in height of them.
Furthermore, when the float 4 inclines with its center round bore 3 abutting on the side surface of the guide 2, the float 4 may adhere to the guide 2 by the effect of surface tension of oil on the abutting center bore portion of the float 4 as shown in FIG. 14 and therefore it cannot smoothly move following the changing level of oil in the case.